1. Technical Field
The present disclosure relates to orthopaedic prostheses and, specifically, to knee prostheses.
2. Description of the Related Art
Orthopaedic prostheses are commonly utilized to repair and/or replace damaged bone and tissue in the human body. For example, a knee prosthesis may include a tibial component and/or a femoral component to replace damaged and/or destroyed bone in the tibia and/or femur. Knee prostheses seek to provide articulation similar to the natural, anatomical articulation of the knee joint.
Total knee replacement (TKR) surgery involves the implantation of several components meant to restore the functionality normally provided by a natural knee. Typical TKR components include a tibial component, a femoral component, and an insert or bearing component disposed between the tibial and femoral components. The insert component is used to provide an appropriate level of friction and contact area at the interface between the femoral component and the insert. For example, a high degree of conformity between the convex curvature of the femoral component and the corresponding concave curvature of the tibial insert results in a large area of contact and correspondingly low pressure at the interface. However, this high degree of conformity also increases the magnitude of shear forces between the femoral component and insert during articulation between the insert and femoral component, i.e., during flexion and extension of the knee.
In certain TKR prostheses, which may be referred to as “posterior stabilized” prostheses, a cam positioned at the posterior portion of the intercondylar fossa of a femoral component cooperates with a spine formed in a tibial component to guide or constrain motion within certain predefined boundaries. For example, posterior stabilized prostheses may include a spine integrally formed with a tibial bearing insert (or “meniscal component”) which interacts with a cam formed in a femoral component to promote femoral roll back during flexion of the TKR prosthesis. Typically, the articular interface between the femoral component and tibial insert is of low- or medium-congruency to facilitate the sliding motion which occurs during femoral rollback. Posterior stabilized prostheses are appropriate where the posterior cruciate ligament (PCL) is torn or otherwise damaged, or where the PCL is resected during surgery.
In addition, some knee prostheses include posterior-facing structures within a femoral component which engage an anterior-facing surface of the tibial spine when the knee prosthesis is in a “full extension” or “hyperextension” configuration. In these systems, interaction between the femoral component and spine operates as a physical stop against extension of the knee prosthesis past a predetermined level of extension. Such “hyperextension stops” typically result in full engagement of the femoral component and tibial spine at a single point of extension or hyperextension, or within a narrow range of extension or hyperextension, as opposed to engaging throughout a range of motion.
On the other hand, some femoral components interact with a tibial spine over a range of knee prosthesis motion in order to facilitate a particular motion profile throughout a “guided” range of motion. In some instances, for example, interaction between a femoral component structure and a tibial spine may be used to mimic a natural motion profile within certain motion ranges. One such motion profile, for example, might mimic external rotation of the femoral component in deep flexion. A guided motion profile may also mimic “femoral roll back”, i.e., the posterior translation of the femoral/tibial articulation contact point during flexion.
In still other TKR knee prosthesis designs, a tibial insert may be allowed to move within a limited range of motion upon the proximal tibial plate of the tibial component. In these “mobile bearing” knee prosthesis systems, translation of the femoral component relative to the tibial component may be accomplished by movement at the interface between the tibial insert and the tibial plate, rather than at the interface between the tibial insert and the femoral condyle.